From German Patent Application No. DE 195 38 791, a fuel injector for fuel-injection systems of internal combustion engines is known which has a piezoelectric device guided in a valve member whose piezoactuator, which cooperates with a needle-type valve-closure member, is fixedly clamped in an end piece facing away from the closure member and, upon activation, lifts the valve-closure member off from a valve seat. The end piece is fixedly connected to the valve member tightly surrounding the piezoactuator. The valve member is made of a material that compensates for the temperature-related longitudinal changes of the piezoactuator at least approximately.
In one embodiment, a fuel injector is known from German Patent Application No. DE 195 38 791 whose valve body is embodied as a two-part sleeve, which has sleeve parts that are arranged coaxially with respect to one another. These sleeve parts are situated in such a way that they follow each other in an imaginary longitudinal direction of the fuel injector and are made of materials having different thermal expansion coefficients, the materials being steel and Invar, for example. The sum of the temperature-related expansions of these two sleeve parts corresponds to the temperature-related expansion of the piezoactuator and of connection elements to the valve-closure member.
Disadvantageous in this known related art is that the sleeve, which has very low thermal expansion or none at all and is made of an expensive material, must fulfill all the functions of a valve member as well. Thus, the sleeve is not only subjected to a pressure load, but to a tensile load as well and must therefore be appropriately manufactured and include affixation means. This means that threads or similar devices must be provided, and increased material is required since these affixation means take up unit volume. Furthermore, it is disadvantageous that the sleeve must be redesigned when the overall length or the material properties of the actuator are changed even slightly, since it is solely the effective length of the sleeve that determines the measure of the thermal overall expansion.
From European Patent Application No. EP 0 869 278, a fuel injector having a controllable actuator is known, which is inserted in an actuator housing fixedly connected to a valve body. The actuator is in operative connection with a valve needle, and a valve-closure member, which cooperates with a valve-seat surface to form a valve-sealing seat, is formed on the valve needle. The material of the actuator housing has a thermal expansion coefficient which is nearly equal to the thermal expansion coefficient of the piezoelectric actuator. The actuator housing is inserted in a recess of the valve body and screw fitted with the valve body via a flange situated approximately in the middle of the longitudinal extension of the actuator housing. The temperature-related expansion of the actuator and the transmission elements up to the valve-closure member corresponds to the temperature-related expansion of the valve body and of the segment of the actuator housing running from the flange up to an end element on which the actuator is braced.
Disadvantageous in the indicated related art is that it offers no way to avoid having to form the actuator-housing attachment on the valve member in the material having low thermal expansion. Producing a flange, for example, requires a blank in the manufacture, the blank having at least the diameter of the flange, thus causing considerable material waste. Because of the special material, this is very expensive.
Moreover, here, too, it is disadvantageous that no provision is made for precise regulation, and a change in the dimensions or properties of the actuator requires a new design and a modification of the component of the actuator housing.